document docsrv target

docs/documenting.md

@@ -2,8 +2,6 @@ Documentation of the `master` branch is deployed to Netlify automatically.
 
 To host or develop locally:
 
-- install python3 and pip
-- `pip install mkdocs mkdocs-material`
-- `mkdocs serve` and visit [localhost:8000](http://localhost:8000).
+- `make docsrv` and visit [localhost:8000](http://localhost:8000).
 
 The file `runtime.txt` is necessary to tell Netlify to use Python3.